1. Field of the Invention
The present invention is related to a capacitor-loaded type single- pole planar antenna; and especially to such a planar antenna suitable for sticking as a plane on the surface of the housing of communication equipment such as a mobile phone, functioning as a dual-frequency transceiver antenna.
2. Description of the Prior Art
As the mobile phones were emerged in the markets in early days, most of them used exposed coils of spiral structure as the main elements of antennas. These coil antennas used widely nowadays are divided into two major typesxe2x80x94contractible type and fixed type. No matter what type of structure is used, under normal circumstances, it still protrudes with a specific length out of the body""s top surface of a mobile phone. The conventional coil antennas become more and more unsuitable for the design requirement of the miniaturized mobile phones, hence microstrip antennas have been developed. Because the characteristics of the microstrip antennas are flatness and small space demanding, such antennas certainly will become the mainstream products for the miniaturized mobile phones.
A microstrip antenna of the early stage, as disclosed in U.S. Pat. No. 3,921,177 or 3,810,183, usually consists of a round or rectangular thin metal sheet, and dielectric substance is stuffed between it and the ground; but these microstrip antennas are only compatible with narrower bandwidths. Taiwan Patent No. 81108896 (U.S. Patent Application Ser. No. 07/798700) provided a microstrip antenna with diminished size and broadband, however the defects of this kind of antenna are to install the spiral antenna elements on separate ground boards, and to stuff dielectric and loading material of specific thickness between them. The size of the whole antenna was still hard to be further reduced.
And if the antenna is installed on the housing of a set of communication equipment, it will cause an end leakage and thus generate an end effect between the planar antenna and the interior grounding metal shield used for preventing electromagnetic interference (EMI) inside the communication equipment. Generally speaking, the larger the distance between the antenna and the grounding metal shield is, the more obvious end effect shows, the harmonic oscillation frequency of the antenna accordingly is lowered, this has become the problem yet to be solved.
The prime object of the present invention is to provide a capacitor-loaded type single-pole planar antenna, which can be stuck flatly on the housing of the communication equipment as a transceiver antenna of 900 MH and 1800 MHz.
In order to achieve the above mentioned object, the present invention is made a capacitor-loaded type single-pole planar antenna by processing the xc2xcxcex antenna which is a low band antenna to make its predetermined length tortuous in pursuance of the size of the installation space for it, and by connecting a capacitor with a minimal capacity value to a length of open stub used as an impedance matching adjuster and being able to increase the bandwidth at the tailing end of this low band antenna. Then, when the band is mainly 900 MHz, the open stub and the capacitor with the minimal capacity value will be the capacitor loaded circuit, and if the band is mainly 1800 MHz, the low band antenna and the capacitor with the minimal capacity value will be the capacitor loaded circuit, so as to be suitable for two different frequencies 900 MHz and 1800 MHz.
The novelty and other features of the present invention will be apparent after reading the detailed description of the preferred embodiment thereof in reference to the accompanying drawings.